1. Field of the Invention
This application is a continuation-in-part of application Ser. No. 07/385,067, filed July 26, 1989 by the same inventor.
The present invention relates to hollow-bodied acoustic guitars. More particularly, it relates to hollow-bodied acoustic guitars with electric pickups The present invention provides an acoustic-electric guitar that doesn't feed back, as is common with known acoustic-electric guitars. Conventional acoustic-electric guitars usually have the electric pickup mounted on the top sound plate or over the sound hole of the guitar. Sound energy from an amplified speaker causes the hollow body to resonate, thus causing the guitar to give off booming feedback back to the speakers.
2. Description of the Prior Art
Stringed acoustic instruments such as guitars need to have lightly-built bodies in order to resonate properly and give a loud, pleasing sound. This is especially true of the spruce top plate, which is the most important acoustic element. On the other hand, these instruments must be robust enough to withstand ordinary use, and to resist the tension in the strings. This tension can lead to warping, detuning, and breakage if the instrument body is not strong enough. An idea of the force involved can be gotten from the fact that the nylon strings of classic guitar would support a 120-pound weight at concert pitch. Steel strings are under much more tension. Multiple strings, as on mandolins and 12-string guitars, require careful bracing of the top plate.
One solution to this problem is the use of a central interior neck extension. This member, extending from the neck to the block opposite, adds some mechanical support to the body.
A number of U.S. patents teach the use of a longitudinal interior neck extension. Among them are Fender, 3,302,507; Prescott, 2,660,912; Quattrociocche, 2,204,150; Montoya, 653,521; Forrest, 607,359; and Larson, 1,889,408.
Acoustic guitars sometimes include electric pickups so that they can function either way, acoustically or electrically. The pickups are usually either magnetic coils which sense the steel string by varying magnetic flux, or crystal or piezoelectric pressure sensors mounted under the bridge.
The magnetic pickups must be mounted close to the strings, or the very weak flux changes will not give sufficient volume. For this reason magnetic pickups have been mounted on the top plate, under the strings. Problems sometimes occur with this mounting when mechanical vibrations of the spruce top plate influence the electrical output of the pickups. The top plate vibrates more than any other part of an acoustic guitar.
This mechanical influence may distort the electrical output of the pickups. Also, since the thin top plate vibrates in response to ambient sound, the loudly amplified pickup output from nearby speakers can cause the top plate-mounted pickup to act as a microphone, leading to the loud squeals called "feedback".
Carriveau, in U.S. Pat. No. 4,913,024, discloses an acoustic-electric guitar with back and sides formed by routing wood from a thick plank, as in making a dugout canoe. The space is covered with a top plate which acts as a sound board. Pickups are mounted through openings in the sound board. It is unclear from the disclosure how the pickups are fastened in place; they apparently are adhered to the sound board itself, since Carriveau states in col. 6, lines 9-16, that the chamber within is acoustically sealed, which implies either adhesive or caulking between the pickups 100, 104 and the sound board 30. Alternatively, the figures may be interpreted to show that the pickups are mounted to longitudinal braces, which braces are mounted to the underside of the sound board. Under either interpretation, the pickups are directly connected to the vibrating sound board and are subject to mechanical influence. Thus Carriveau does not teach a method of isolating magnetic pickups from the top plate.
Law, in U.S. Pat. No. 3,780,202, teaches the use of a magnetic pickup mounted on a bracket riding on an interior neck extension. The pickup senses the vibrations of steel banjo strings through the banjo head or skin, which ordinarily has no magnetic properties to interfere with the pickup's sensing of the string vibrations.
Since a banjo head cannot be pierced without destroying its tone, there is seen no suggestion in the Law patent of mounting a pickup on an interior neck extension, and protruding the pickup through the face of the instrument adjacent the strings.
The position of Law's pickup is highly adjustable. This is intended to provide various timbres and volumes. It is well known in the art that magnetic pickups produce various timbres depending upon their distance from the bridge, and various volumes depending upon their distance from the strings. The Law pickup bracket allows these variations by translating the pickup, and also allows both timbre and volume differentials between individual strings by rotating the pickup.
The Law device avoids feedback, in all positions of the pickup, by the mechanical isolation of the pickup on a massive, rigid, braced neck extension not directly connected to the vibrating sounding head. The isolation is very great unless the pickup actually touches the skin of the head. Since touching would ruin the tone of the instrument by damping the head, as well as lead to feedback, this is clearly not intended.
The timbre and volume modifications of sound in Law's invention is unrelated to the feedback problem: there are many pickup positions where there is no touching, and no feedback; adjustability among these positions to vary the timbre is unrelated to feedback, in regard to which all the positions are the same.
Loar, in U.S. Pat. No. 2,020,557, shows a guitar with a transverse member running across the wide lower bout of the guitar, the member not touching either the front or back sound plates. The transverse member supports a magnetic coil device which responds to mechanical vibrations. The device is placed directly below a hole through the front plate (sound board). A special bridge is placed directly above the hole. Adjustable-length rods extend through the hole from the bridge to the device. By adjusting the length of the rods, the strings may be made to vibrate the sound board, the device, or both, by pressing the rods against the device or by lifting the bridge off the sound board.
These rods have no electrical function; they merely transmit vibration from the bridge to the device beneath. Thus, Loar does not teach a magnetic device or pickup extending through the sound board.
DiMarzio, in U.S. Pat. No. 4,227,434, shows a pickup bracket for mounting the pickup within a round sound hole on the front plate of a guitar. The pickup extends through the hole.
Other commercially-available devices clip a pickup onto one edge of a sound hole. These pickups are merely microphones.
Thus, the prior art does not show any method of mounting magnetic or electrical pickups adjacent the strings of an acoustic guitar in such a way that the pickups are isolated from vibrations of the guitar top plate, to avoid tonal influence and feedback. In particular, the prior art does not show vibration-isolated mounting on a neck extension.
Accordingly, it is one object of the present invention to provide an acoustic-electric guitar that reduces amplification feedback;
It is a further object of the present invention to provide an acoustic-electric guitar with electric pickups mounted on a neck extension;
It is a still further object of the present invention to provide an acoustic-electric guitar with apertures in the top sound plate to allow access to the electric pickups and control panel; and
It is another object of the present invention to provide an acoustic-electric guitar neck extension with a preformed nipple to fit flush with a cutaway portion of the guitar.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.